Correcting perspective distortion for an angled projector (Keystone effect)
I don't know whether this suits, you might be wanting more of a simulation of real lenses. But we have an unusual advantage here in CG-world .. the projector can know how far away it is from the points it's projecting onto, via a Ray Length output of a Light Path node.

By similar triangles, (multiplying the normal by the ray-length) the spherical look-up, using the lamp's normal direction, can be corrected back to an orthogonal look-up into the texture, correcting the keystone.

Assuming the lamp is rotating around its X axis, that angle can be used in a driver to correct the aspect ratio of the resulting rectangle.A sine is taken only because the wall is at 90 degrees. If the lamp was projecting onto the floor, or the lamp was parented to a screen with its Z pointing towards it, that would be a cosine.



I've also set the lamp's falloff to 'Constant', so the image is evenly bright. You may want to switch that out.